The present invention relates to a method of manufacturing a color filter suitable for solid-state image sensing devices, liquid crystal displays and the like.
Electronic devices such as CCD (Charge Coupled Device) type color solid-state image sensing devices and color liquid crystal displays each have on its front face a color filter in which filter elements of red, green and blue or cyan, yellow, and magenta are disposed in a specific array, for example, a specific stripe or mosaic pattern.
An example of a CCD type color solid-state image sensing device will be described with reference to FIG. 1 in which a light receiving portion of the device is schematically shown in cross-section. In this example, a p-type first well region 2 is formed on a principal face side of an n-type semiconductor substrate 1, and an n-type doped region 3 for forming a photoelectric transfer element such as a photodiode is formed on a portion of the well region 2 in which the light receiving portion is to be formed and a p-type highly doped positive charge storage region 4 is formed on a surface of the doped region 3, to form a light receiving portion 5. A number of the light receiving portions 5 are formed on the semiconductor substrate 1 in such a manner as to be arranged along the horizontal and vertical directions. A common vertical shift register having a CCD configuration is formed adjacently to a sequence of those of the light receiving portions 5 arranged in the vertical direction. The vertical shift register is composed of an n-type transfer region 8 formed on a p-type second well region 7 and a transfer electrode 10 formed on the transfer region 8 through an insulating layer 9 made from SiO.sub.2 or the like. A plural sets of the transfer electrodes 10, insulated from each other in the vertical direction, are arranged. When a clock voltage is applied between the transfer electrodes 10 of each set, the corresponding light receiving portion 5 generates charges in correspondence with the received light amount. The charges thus generated from the light receiving portions 5 are fetched therefrom and are sequentially transferred in the vertical direction.
A p-type highly doped channel stop region 14 is formed on the semiconductor substrate 1 at such a portion as not to allow reception and transfer of charges.
A light shielding film 11 formed of an Al layer or the like, which has a light receiving window 11w located directly over the light receiving portion 5, is formed substantially over the entire upper surface of the solid-stage image sensing device.
A protective film 12 made from a light transmissive material such as SiO.sub.2 or SiN is formed over the entire surface of the light shielding film 11, and a color filter 13 is formed on the protective film 12.
FIG. 2 shows an example of an arrangement pattern of filter elements of the color filter 13. In this example, red filter elements R, green filter elements G and blue filter elements B, or cyan filter elements C, magenta filter elements M and yellow filter elements Y are arranged over the corresponding light receiving portions 5 in a mosaic pattern.
Various methods of manufacturing such a color filter have been proposed. In particular, a method of using as color filter elements a pattern formed of a dye containing positive photoresist (type in which an exposed portion is desirably soluble in a developer) is suitable for manufacturing a color filter having a fine pattern.
In this method, a base on which a color filter is to be formed, for example, an upper surface of the above-described solid-state image sensing device is coated with a positive type photoresist containing a dye of a first color, for example, red. The photoresist is subjected to pattern-exposure by exposing the entire surface thereof except for portions for forming desired red filter elements R. The exposed portions are then removed by development, to pattern the photoresist. A photosensitive agent contained in the photoresist is bleached, and the photoresist is heated for hardening, to form red filter elements R. Subsequently, the entire surface of the base containing upper surfaces of the red filter elements R is coated with a positive type photoresist containing a dye of another color, for example, green. Thereafter, the above-described procedure is repeated, to form green filter elements G. Similarly, blue filter elements B are formed using a positive type photoresist containing a blue dye in accordance with the above-described procedure. In this manner, a color filter in which the filter elements R, G and B are arranged as shown in FIG. 2 is obtained.
In the method of manufacturing a color filter, in which a pattern of a photoresist containing a dye of each color is directly used as filter elements of the color, a base is sequentially coated with a plurality of photoresists containing dyes of desired colors. In this case, when a previously formed photoresist layer patterned into filter elements is coated with a photoresist containing another dye, the dye is possibly permeated in the previously formed photoresist layer, resulting in color mixture. To avoid occurrence of such a color mixture, the patterned photoresist must be sufficiently hardened to enhance a solvent resistance for preventing contamination of another dye. In general, a photoresist layer is hardened by heating it at a temperature in a range of 120.degree. C. to 150.degree. C.
On the other hand, with respect to the method of manufacturing a color filter in which a pattern of a photoresist containing a dye is directly used as filter elements, there has been proposed a method of manufacturing a color filter in Japanese Patent Publication No. Hei 7-111485, in which a positive type photoresist containing a dye in a large amount of 10 to 50% is used for obtaining excellent color filter characteristics.
Incidentally, a patterned photoresist containing a large amount of dye, which is obtained by the above-described general hardening treatment carried out by heating the photoresist at about 150.degree. C., fails to exhibit a sufficient solvent resistance, because the added dye has a relatively small molecular weight. As a result, a dye of another color having a small molecular weight is liable to be mixed in the previously hardened photoresist, leading to reduction in color purity. To avoid such an inconvenience, it may be considered to-increase the hardening temperature at a value more than 150.degree. C.; however, in this case, a photoresist is deformed. In particular, a photoresist containing a dye in a large amount tends to be significantly deformed because the added dye is generally lower in melting point than a binder resin.
The deformation of a photoresist, particularly, having a fine pattern, causes problems in degrading optical and mechanical characteristics, thereby reducing the reliability and increasing the incidence of defective.